Jenn,
Probably in the realm of idle speculation here.
Field of view would be dependent on focal length just like visible
light.
Resolution is also a function of the size of the pinhole based on the
standard circle of confusion arguments, The smaller the pinhole, the
greater f is, therefore the sharper the image.
On the lower limit, optimal pinhole size is a function of the
wavelength and focal length. Since the wavelength of gamma rays is so
short, it would be pretty hard to get a hole small enough for this to
come in to play.
The thick piece of lead is going to be your biggest problem. The ideal
pinhole is in a planar surface. In actual practice, this means as
thin a material as is opaque to the radiation involved. I 'm afraid I
don't know the arguments, but when the hole becomes a tunnel, image
quality fails, first because it restricts the field of view (strictly a
geometry thing again) , and secondly because of internal reflections
inside the tunnel (but I don't think gamma rays will reflect normally
off a lead surface). There's gotta be some other reason also, the
Victorian authors I've read make a big deal about the thinness of the
material.
Some of the first high energy astronomy detectors were clusters of
tunnels like this that didn't form an image exactly, just restricted
the field of view so much that they detected that there was a source of
light somewhere in the direction the tunnel was pointing.
Interesting idea though.
On Tuesday, May 13, 2003, at 12:01 PM, jennem...@mad.scientist.com
wrote:
Hello,
I'm working on a project that I thought might interest people here and
I could certainly use input from people with more experience than I.
I am working as a Medical Physicist for my summer Co-op position. One
of the projects I am working on is an attempt to use a x-ray
flouroscopy screen and a thick piece of lead with a hole drilled
through the center to try and image the position of a point source of
radiation in a radiation therapy procedure. The radiation used is
gamma-radiation which is an electromagnetic wave like light so it has
most of the same properties.
I am trying to optimize the Field of View and the Resolution and can't
find _any_ resources for pinhole imaging with the pinhole in a thick
material. (The thickness is required, otherwise the strength of the
radiation will over-expose the screen and all we will see is white.)
Any knowledge, links or even idle speculation would be appreciated.
Thanks,
Jenn
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